Anodic Protective Seal in a Blowout Preventer

ABSTRACT

An anodic sacrificial seal element is installed at vulnerable regions of a blowout preventer. A zinc cylinder, for example, is included at the well-bore pressure side of a bonnet which seals around a rod as it extends through a bonnet which joins an actuator to the body of the BOP. Similarly, a zinc O-ring may be used in a seal groove provided between the bonnet and the body of the BOP. In this way, the high electropotential of the material from which the additional seal element is made is oxidized first, before any attack on the BOP material, thereby increasing the time period between maintenance events on the BOP.

DESCRIPTION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/61 8,489 filed Oct. 13, 2004.

FIELD OF THE INVENTION

The present invention relates generally to the field of metal systemssubjected to harsh, corrosive environments, such as for example blowoutpreventers for tubing, and, more particularly, to a sacrificial anodicseal element for use in such an environment on such a metal system.

BACKGROUND OF THE INVENTION

The use of a blowout preventer in drilling, completion, workover, andproduction of oil and gas wells is well known. Such a blowout preventergenerally includes a housing with a bore extending through the housing.Opposed chambers extend laterally on either side of the bore in thehousing and communicate with the bore. Rams within the chambers areconnected to rods that are supported for moving the rams inwardly intothe bore to close off the bore. The rods also serve to retract outwardlyfrom the bore to open the bore.

A volume is provided within a bonnet to provide a space to receive theram when the rod is pulled back away from the bore. This volume istypically filled with a stagnant liquid having corrosive properties.Over time, the bonnet material which defines the volume begins tocorrode and eventually the entire actuator assembly, including the ram,must be refurbished or replaced. This maintenance evolution costs moneyand causes down time for the well.

Relatively inaccessible blowout preventers, such as those mounted on theocean bottom, one typical solution involves coating BOP surfaces whichare subjected to the stagnant corrosive fluid with a layer of Inconel®and machining the Inconel® to design tolerances. However, this solutionis expensive and is not tolerable for most BOPs and applications.Inconel® is a registered trademark of Inco Alloys International, Inc.

Thus, there remains a need for a structure which eliminates or at leastslows the corrosion of material of the bonnet of a BOP and similarstructures. The present invention is directed to filling this need inthe art.

SUMMARY OF THE INVENTION

The present invention addresses these and other needs in the art byproviding an anodic sacrificial seal element at vulnerable regions of ablowout preventer. A zinc cylinder, for example, is included at thewell-bore pressure side of a bonnet which seals around the rod as itextends through the bonnet. Similarly, a zinc O-ring may be used in theseal groove provided between the bonnet and the body of the BOP. In thisway, the high electropotential of the material from which theadditional, sacrificial seal element is made is oxidized first, beforeany attack on the BOP material, thereby increasing the time necessarybetween maintenance events on the BOP.

These and other features and advantages of this invention will bereadily apparent to those skilled in the art from a review of thefollowing detailed description along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobject of the present invention are attained and can be understood indetail, more particular description of the invention, briefly summarizedabove, may be had by reference to embodiments thereof which areillustrated in the appended drawings.

FIG. 1 is an elevation section view of an actuator and coiled tubing ramconstructed in accordance with the teachings of the present invention.

FIG. 2 is a detail view of an O-ring seal between the body of the BOPand the bonnet.

FIG. 3 is a detail view of an anodic seal element around the rod of theram assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to all of the drawing figures, FIG. 1 illustrates thepresent invention in its intended environment. While the presentinvention is illustrated at particular point in a BOP, it will beimmediately apparent to those of skill in the art that the invention maybe applied in other regions of this and similar structures havingpressure seals and stagnant, corrosion fluid captured within avulnerable metal body.

An actuator assembly 10 includes a cylinder body 12 enclosing a cylinderchamber 14 having a piston 16 therein. A close port 18 directs hydraulicfluid pressure to one side of the piston 16 to close the ram, and anopen port 20 directs hydraulic fluid pressure to the other side of thepiston to open the ram. The piston 16 connects to a rod 22 whichterminates at a ram head 24 which connects to a ram 26, for example,although any other appropriate type of ram head may be used.

The ram 26 moves within a body 28 of a blowout preventer which isaligned along a center axis 30. It is to be understood that a similarram and associated actuator assembly (not shown in FIG. 1) arepositioned opposite the ram 26 to enclose a tubular, such as a coiledtubing 32, passing through a bore 33 of the blowout preventer. Uponactuation, the ram 26 closes in around the coiled tubing 32.

The rod 22 penetrates to well-bore pressure through a bonnet 36. A sealmember 38 seals between the rod 22 and the bonnet 36. Seals in thisapplication are commonly known in the art. The present invention,however, provides an anodic sacrificial element 40 between the sealmember 38 and the bore 33 of the BOP. The element 40 is preferablyformed of zinc which has an electropotential of +0.758, far higher thanthat of iron, which has an electropotential of +0.441, although anotherappropriate material may be used so long as its electropotential ishigher than that of the material from which the BOP is made.

The bonnet 36 defines a chamber 42 to receive the ram 26 when the ram isretracted. This chamber 42 serves as a reservoir of stagnant fluid,typically well-bore fluid, over extended period when the BOP isinactive. This stagnant fluid is an electrolyte creating a corrosiveatmosphere for the materials of the BOP. The anodic element 40 thuscorrodes in order to save the BOP materials.

An O-ring seal 44 is also commonly used between the bonnet 36 and thebody 28 of the BOP. In the present invention, however, an anodic sealelement 46 is provided between the seal 44 and the well-bore 33 toprovide an anodic protective function like that of the element 40.

It should also be apparent to those skilled in the art that, while theforegoing has emphasized the present invention in the environment of ablowout preventer, the present invention should not be perceived aslimited to only this application. The present invention may be adaptedto use in any seal between two moving metal elements which must exist ina corrosive environment.

The principles, preferred embodiments, and mode of operation of thepresent invention have been described in the foregoing specification.This invention is not to be construed as limited to the particular formsdisclosed, since these are regarded as illustrative rather thanrestrictive. Moreover, variations and changes may be made by thoseskilled in the art without departing from the spirit of the invention.

1. A blowout preventer actuator assembly joined to a blowout preventerbody, the assembly comprising: a bonnet; a cylinder body coupled to thebonnet and enclosing a cylinder chamber having a piston therein; a rodconnected to the piston at one end and to a ram head at the other end;and a first anodic seal element between the bonnet and the rod.
 2. Theassembly of claim 1, wherein the first anodic seal element is made ofzinc.
 3. The assembly of claim 1, further comprising a first pressureseal element adjacent the first anodic seal element.
 4. The assembly ofclaim 1, wherein the first anodic seal element defines a cylinder. 5.The assembly of claim 1, further comprising a second anodic seal elementbetween the bonnet and the blowout preventer body.
 6. The assembly ofclaim 5, wherein the second anodic seal element is made of zinc.
 7. Theassembly of claim 5, wherein the second anodic seal element is made of amaterial having an electropotential higher than the material from whicheither the bonnet or the rod are made.
 8. The assembly of claim 5,further comprising a second pressure seal element adjacent the secondanodic seal element.
 9. The assembly of claim 8, wherein the secondpressure seal element and the second anodic element are each formed inthe shape of a ring.
 10. A seal element between first and second metalcomponents comprising an anodic member having an electropotential higherthan either of the first and second metal components and positionedadjacent a pressure seal element.